In the related art, in an IC chip including a voltage regulator, an output condenser is connected to an output terminal of the voltage regulator parallel to a load. Generally, an electrolytic condenser or a tantalum condenser is used as the output condenser, but recently, a stacked ceramic condenser, which is compact and able to have a large capacity, has been developed and put into practical use.
The electrolytic condenser, the tantalum condenser, and the stacked ceramic condenser have different equivalent series resistances (abbreviated to be “ESR” where necessary). For example, the equivalent series resistance of the electrolytic condenser is 0.1-100Ω, the equivalent series resistance of the tantalum condenser is 0.01-10Ω, and the equivalent series resistance of the ceramic condenser is 0.001-0.1Ω. Due to the different equivalent series resistances of condensers connected to the output terminal, sometimes phase compensation of the voltage regulator cannot be performed appropriately depending on types of the condensers.
Generally, the phase compensation of the voltage regulator is also carried out in the circuits of the voltage regulator; when the output condenser is combined with the voltage regulator, a zero-point appears in the frequency characteristic curve, and consequently, a phase margin appears in a region where the frequency gain is near 0 dB. When the ceramic condenser, which has a small equivalent series resistance, is connected to the voltage regulator, however, the above-mentioned zero-point in the frequency characteristic curve moves to the high frequency side, the phase margin disappears in the region where the frequency gain is near 0 dB, and this causes oscillation. To solve this problem, when a ceramic condenser is used as the output condenser, a resistor of a resistance from 0.001 mΩ to 1.5Ω is connected to the ceramic condenser in series to cover the lack of the equivalent series resistance.
For example, Japanese Laid Open Patent Application No. 2003-86683 discloses a technique in this field.
FIG. 11 is a circuit diagram illustrating an example of a semiconductor device of the related art, in which an IC chip having a voltage regulator is installed in a chip-size package (CSP).
The semiconductor device shown in FIG. 11 includes a CSP 101, a load 102, a direct-current power supply 103 serving as an input power supply, a semiconductor chip 110 having a voltage regulator, and a ceramic condenser C121.
The equivalent series resistance of the ceramic condenser C121 is represented by Resr, and the capacitance of the ceramic condenser C121 is represented by Co.
A resistor R113 in the CSP 101 is for compensating for the equivalent series resistance of the ceramic condenser C121. The resistor R113 is formed by employing the wiring resistance of the rerouting wires disposed in an interposer of the CSP 101, and is formed between an output terminal 113 of the semiconductor chip 110 having the voltage regulator, and an output terminal OUT of the CSP 101.
Since the resistor R113 is formed in the CSP 101, even when the output condenser C121 is a ceramic condenser, the phase compensation of the voltage regulator can be carried out appropriately, and oscillation can be prevented even without the load 102 being connected to the output condenser C121 in series.
However, since the resistor R113 is formed between the output terminal 113 of the semiconductor chip 110 and the output terminal OUT of the CSP 101, when an output current through the load 102 becomes large, the voltage drop across the resistor R113 increases and cannot be neglected any longer. For this reason, the resistance of the resistor R113 has to be relatively small, for example, the resistance of the resistor R113 is in a range from 10 mΩ to 200 mΩ. Because of such an output condenser C121, the phase margin may become small, and furthermore, in applications involving large currents, the voltage drop across the resistor R113 having such a small resistance value can still become too large to be neglected.
In addition, since the output condenser C121 is present as an external part, the mounting area cannot be reduced very much, furthermore, from the point of view of fabrication and management, work load of inventory control and mounting of the output condenser C121 are required, and from the point of view of stability of the output voltage, a user has to consider matching the output condenser C121 and the voltage regulator. Due to this, quality and ease of use of the device cannot be improved sufficiently.